Studies of receptors, ion channels, and other membrane proteins require a solid understanding of the structural principles of these important biomolecules. Membrane protein structure is, however, a very challenging field. The structures of only three types of transmembrane proteins have been determined to moderate or high resolution during the last two decades, a period during which the amino acid sequences of hundreds, if not thousands, of membrane proteins have been reported. As a result, the creation of structural models to serve as guides for studies of receptors, channels, and other membrane proteins has become crucially important. This book has been assembled in order to share the experiences and findings of expert researchers in protein structure and structure-prediction methods as well as membrane biophysics and lipid physical chemistry, whose work establishes the basis for the development of suitable model structures. The reviews presented here emphasize fundamental ideas and provide an entry to the diverse and complex literature. The four major sections deal with the general nature of the membrane protein structure problem, biochemical and molecular biological approaches to protein topology, direct structural methods, and model and physicochemical approaches. The work will be of interest to physiologists, cellular and molecular biologists, biophysicists, and biochemists working on the function of membrane proteins such as receptors, ion channels, and transporters, as well as senior graduate students and independent investigators.